Python: Fix async functions that return external types (#2659)

The issue was that we were using the same name for both the local and
external types, which lead to the one of them being lost when they were
de-duped.

Author: bendk

uniffi_bindgen/src/bindings/python/pipeline/external_types.rs

@@ -59,6 +59,18 @@ pub fn pass(namespace: &mut Namespace) -> Result<()> {
             _ => (),
         };
     });
+    // Transform RustBuffer namespaces to concrete Python module names
+    namespace.visit_mut(|ffi_type: &mut FfiType| {
+        if let FfiType::RustBuffer(Some(ref mut namespace)) = ffi_type {
+            match namespace_config.external_packages.get(namespace) {
+                Some(package_name) if !package_name.is_empty() => {
+                    *namespace = package_name.clone();
+                }
+                _ => (),
+            }
+        }
+    });
+
     namespace.imports.extend(module_imports);
     Ok(())
 }

uniffi_bindgen/src/pipeline/general/ffi_async_data.rs

@@ -42,6 +42,11 @@ fn generate_async_data(crate_name: &str, ffi_return_type: Option<&FfiTypeNode>)
         None => "void",
         ty => panic!("Invalid future return type: {ty:?}"),
     };
+    let struct_crate_name = match &ffi_return_type.map(|ffi_type| &ffi_type.ty) {
+        Some(FfiType::RustBuffer(Some(rust_buffer_crate))) => rust_buffer_crate,
+        _ => "",
+    };
+
     AsyncData {
         ffi_rust_future_poll: RustFfiFunctionName(format!(
             "ffi_{crate_name}_rust_future_poll_{return_type_name}"
@@ -56,11 +61,11 @@ fn generate_async_data(crate_name: &str, ffi_return_type: Option<&FfiTypeNode>)
             "ffi_{crate_name}_rust_future_free_{return_type_name}"
         )),
         ffi_foreign_future_result: FfiStructName(format!(
-            "ForeignFutureResult{}",
+            "ForeignFutureResult{struct_crate_name}{}",
             return_type_name.to_upper_camel_case()
         )),
         ffi_foreign_future_complete: FfiFunctionTypeName(format!(
-            "ForeignFutureComplete{return_type_name}"
+            "ForeignFutureComplete{struct_crate_name}{return_type_name}"
         )),
     }
 }